This invention relates to a square focal plane shutter, in which front and rear blade groups, each consisting of a plurality of shutter blades, are formed with a metal material. More particularly, the invention is concerned with a structure of each shutter blade constituting the focal plane shutter.
In the focal plane shutter manufactured by conventional techniques, the plate material for the shutter blade has been fairly thick at its pivotal connection, with an operating arm or at its cam groove so as to sufficiently withstand the driving force from a drive mechanism. The plate thickness is uniform throughout the shutter blade, causing the inertia of the shutter blade to be large. As a consequence, there is a disadvantages in that: shock at the termination of the shutter blade movement and load at the time of the shutter charging operation (an operation to accumulate driving force in the shutter drive mechanism) are large.